JKav

(Note, this is on my bone stock 2005 G55 - M113K w/ 722.6 - and not an E, but you guys are the most savvy with this powertrain and its various bugs. So here goes... )

I'm noticing during moderate to hard acceleration that, immediately AFTER the upshift, there's a distinct flat spot in the power delivery. The flat spot lasts about a half-second, maybe a second at the very most. Then the power and acceleration resumes as expected. It's not relegated only to the 2-3 or 3-4 shift; it happens after either one (and possibly 4-5, but I don't know for sure).

I want to emphasize that the gearchanges themselves are fine. What I'm observing is happening right after the shift is complete. It's like the supercharger clutch is briefly disengaged, or the throttle is closed (or both) during this period. That's what it feels like; I don't have any datalogging equipment to scrutinize this.

I haven't seen quite this characteristic mentioned elsewhere in this forum. But I'm surely not the first to observe it.

Has anyone experienced this? I would love any insights, or ideas on how to address it.

SICAMG

Sounds like a torque limiting situation from the transmission control from the ECU/TCM program.

JKav

Could be. Is there some issue or reason that would cause the TCU to request the ECU to limit torque after the shift?

JKav

Have any of you guys ever observed this post-shift flat-spot behavior in an E55?

99lightning

sure have all fixed up now, with tcu tune

Sulaco

Has happened to me for years but doesn't do it under tame driving or wide open throttle. Only does it under moderate accelerations so I just ignore it.

the buckle of the supercharger pulley engaging is far more annoying

SICAMG

Tell me about it !! I have a 168-77 stack and if the compressor happens to kick on at the same time it shifts with my race TCU.....WOW !!! Like some one tapped the *** end for sure LOL

rnd_ash

It's not addressable without tuning the tcu. What's happening is the tcu had a very aggressive torque request for the gear shift itself, but also opens up the torque converter clutch. The torque converter clutch is quite laggy by design in its response to pressures sent by the tcu to it, so once your gear shifts complete, the tcu will hold the torque request a bit longer to let the converter finish locking up so you avoid a weird jolt where the engine RPMS may runaway after the shift completed, and then the torque converter closes cause the engine rpm to drop harshly.

Tuning the stock tcu is a good way around this, Mercedes were far too aggressive on the torque request mechanism, likely to let the gearbox survive 20 years on the same ATF out of the factory 😅

Source: I've reverse engineered the egs52 module for my own TCU.

99lightning

rnd ash always has good info and content.

JKav

Thank you, this is exactly the insight I was hoping for.

I'd love a TCU retuning solution that resolves this characteristic. Are you the right guy for this?

machild

Right here: https://mkultraelectronics.com/

rnd_ash

I'm not the right guy for this kind of solution, but as already pointed out, mkultra is a very good tune for these cars!